Bending wave or distributed mode loudspeakers (DML) are described in International application WO97/09842 and other documents in the name New Transducers Ltd. Such loudspeakers may be used in applications where the loudspeaker element has additional functionality. For example, International applications WO97/09843, WO97/09853 and WO01/31971 describe the use of such panels as a ceiling tile, in a projection screen and in a keyboard, respectively.
Furthermore, applications of DML technology have extended to the use of both opaque and transparent loudspeaker panels incorporating touch-sensitive capability. For example International application WO00/54548 describes electronic apparatus incorporating a loudspeaker having a bending wave panel member with a user-accessible surface, an electro-acoustic vibration exciter on the panel member to introduce bending wave energy into the panel member in response to an electrical signal applied thereto, and at least one touch sensitive area on or associated with the said user-accessible surface and responsive to user contact. International application WO01/48684 describes a contact sensitive device comprising a transparent touch sensitive plate mounted in front of a display device.
International Application WO02/51201 describes apparatus comprising a bending wave panel loudspeaker having a bending wave panel defining a surface and an electro-acoustic transducer attached to the bending wave panel to excite bending waves in the panel to produce an acoustic output, an input device forming part of the surface and means for providing force feedback to the input device.
International Application WO01/54450 describes a transducer for producing a force which excites an acoustic radiator, e.g. a panel to produce an acoustic output. The transducer has an intended operative frequency range and comprises a resonant element which has a distribution of modes and which is modal in the operative frequency range. Parameters of the transducer may be adjusted to improve the modality of the resonant element. Such a force transducer is known as a distributed mode actuator or “DMA”.
Touch panels with tactile feedback are known from U.S. Pat. No. 5,977,867 and WO 2008/045694.
It is an object of the present invention to provide an improved touch-sensitive device.